[MERGE] Allow insert_record_stream to partially insert a stream rather than error when there are missing compression parents

[Robert Collins]

Robert Collins has voted tweak.
Status is now: Conditionally approved
Comment:
KndxIndex should error always as its not safe *enough* to come back 
later (as our goal is to do this in two invocations of bzr).

Rather than keeping the buffered entries, push them down to the index 
and keep track of the keys - that is simpler and sufficient as we don't 
need this to be able to work with KndxIndex as those repositories don't 
support stacking anyhow.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090217040630.GA12861%40steerpike.home.puzzling.org%3E
Project: Bazaar